I think 'ga' just indicates that the preceding word/phrase is the subject of the sentence. The 'I' here is not explicitly mentioned, but implied because the speaker is saying it.

admin is right and bellow is more FYI:
Particles play an important role in Japanese language and are small words that indicate relations of words within a sentence.
The Japanese language uses a total of 188 particles while the most important ones are:

wa: adding wa at the end of a word emphasizes that it is the primary subject of the sentence.
ga: suffix to indicate when a word is the secondary subject of a sentence.
o: suffix to indicate that a word is the object of the sentence.

Female Chickens over a year old are known as hens, and younger females as pullets, although in the egg-laying industry, a pullet becomes a hen when she begins to lay eggs, at 16 to 20 weeks of age.